FORUM:

From 8-12 September 1997 a Southern Africa Climate Outlook Forum convened to formulate consensus guidance for the 1997-98 season in southern Africa. The Forum comprised Meteorological Services from SADC (Southern Africa Development Community) countries, and climate scientists from universities and international research institutes. These specialists reviewed the state of the global climate system and its implications for southern Africa. One of the principal factors taken into account is the major El Niņo event on-going in the tropical Pacific Ocean. Recent El Niņo occurrences such as in 1982-83, 1991-92 and 1994-95 resulted in low rainfall across much of southern Africa south of 10 degrees South and disrupted climate patterns around the globe.

Participants at the Forum included representatives of Meteorological Services from eleven SADC countries (Botswana, Lesotho, Malawi, Mauritius, Mozambique, Namibia, Swaziland, South Africa, Tanzania, Zambia and Zimbabwe) and climate scientists and other experts from national, regional and international institutes (Drought Monitoring Centre - Harare; Universities of Witwatersrand, Zululand and Zimbabwe; SADC Food Security Technical and Administrative Unit; Southern Africa Transport and Communications Commission; the World Meteorological Organization; the International Research Institute for Climate Prediction; the U.S. National Oceanic and Atmospheric Administration Office of Global Programs and Climate Prediction Center; the U.S. Agency for International Development; the U.K. Meteorological Office; IMGA/CNR-Bologna; and the World Bank.)

OUTLOOK

The Outlook divides the 1997-98 season into two periods (October-November December and December-January-February-March; Maps A and B respectively). The experts provided probability distributions to indicate the likelihood of below-, near- or above-normal rainfall for each sub-region (see Maps). Users are strongly advised to contact their National Meteorological Service for interpretation of this Outlook and for additional guidance.

In the first period, above-normal rainfall is expected in northern Tanzania (Short Rains) from October through December (Map A). In October through November, rainfall is not expected to depart significantly from normal throughout much of the rest of the region. Although the seasonal onset may be favourable, the possibility of a later downward trend should be considered. One exception is the extreme southern tip of South Africa, where above-normal rainfall is expected. The other is for Mauritius, where below-normal rainfall is expected. Click here for Map Caption with explanation of graphic

December through March is the main rainy season for much of southern Africa. During this period, northeastern regions are expected to experience normal- to above-normal rainfall (Map B). Proceeding southward, there is a distinct trend towards below-normal rainfall which may be significantly below normal over South Africa, southern Mozambique, Lesotho and Swaziland. The northern extent of this region over which significantly below-normal rainfall may occur is uncertain at this stage. Above-normal rainfall is expected for Mauritius.

Much of the Outlook is attributable to the severity and expected persistence of the current El Niņo event into 1998. This and other factors affecting southern Africa's climate were assessed using coupled ocean/atmospheric models, physically-based statistical models and expert interpretation. In some areas there was lack of agreement among the models. In particular, prospects for Malawi, southwestern Zambia and northern Namibia in December through March were uncertain, uncertainties that are reflected in the probabilities and which may be resolved in a later update.

The current status of seasonal to inter-annual forecasting allows prediction of spatial and temporal averages, and may not fully account for all factors that influence regional and national climate variability. This Outlook is relevant only to seasonal timescales and relatively large areas, and local variations may occur.

MAP CAPTION

For each sub-region, during the 1997-98 season, the likelihood associated with the Outlook is represented by the probabilities of that sub-region receiving below normal, near-normal or above-normal rainfall (see keys on Maps), based on model results and expert interpretation. Over many years, rainfall will fall equally frequently into all three categories. For example, between 1961 and 1990 ten of the years will fall into the below-normal category, ten will be normal and ten into the above-normal category.

If all three outcomes were equally likely this current season, the chance for each category would be 33%. A qualitative Outlook of "climatology" indicates that there is no basis for favoring any part of the range of rainfall totals experienced in recent decades. Otherwise, for example in the case of Mauritius during October-November December (Map A), there is a 45% probability in the below-normal category, that is, within the range of the driest third of historically-recorded rainfall; a 30% chance in the near-normal category; and a 20% chance in the above-normal category. Boundaries between sub-regions should be considered as transition zones.

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